1. Field of the Invention
This invention relates in general to output circuits for video tape recorders and particularly to an output signal switching circuit which supplies an output signal from a video tape recorder to other apparatus such as a television receiver.
2. Description of the Prior Art
In commercially available video tape recorders (VTR), during reproduction, a video signal and an audio signal which are reproduced from magnetic tape are remodulated to form a composite RF signal according to a broadcasting modulation system. Such RF signal has a frequency band of a vacant channel, that is a channel where no standard broadcast signals are being received, and such RF signal is supplied to an antenna terminal of a television receiver. The television receiver is capable of receiving not only standard broadcast signals, but also receives the described reproduced signal and operates with the circuit arrangement illustrated in FIG. 1.
FIG. 1 illustrates in block an example of a prior art system wherein an input terminal 51 of a VTR receives an RF signal from an antenna, not shown. The signal applied to the input terminal 51 is supplied to a VTR tuner 52 which is tuned to receive a desired broadcast signal. The tuner 52 produces video and audio signals by demodulating the incoming signal and supplies the video signal to a video processor circuit 53 and the audio signal to an audio processing circuit 54 of the VTR. The video circuit 53 and the audio circuit 54 include tape head systems for recording and reproducing signals.
The video signal and the audio signal from the video and audio processor circuits 53 and 54 are supplied to an RF converter 55 in which they are formed into a signal which complies with the broadcasting system so as to produce an RF signal with the carrier of the vacant channel. The RF signal output of the RF converter 55 is connected to a first fixed terminal 56a of an RF signal changeover switch 56.
The RF signal from the input terminal 51 is supplied to a second fixed terminal 56b of the switch 56 as illustrated. The moveable contact 56c of the switch 56 when connected to terminal 56a supplies the RF output signal to a RF output terminal of the VTR which is connected to an antenna input terminal of a television receiver 70. Switch 56 is designated a TV/video changeover switch.
According to the prior art device during reproduction, the signal is reproduced, for example, from the magnetic tape are or reformed as signals which comply with the broadcasting system by the video processor circuit 53 and the audio processor 54 and are converted to an RF signal at the frequency of the vacant channel by the RF converter 55 and then are fed through the fixed terminal 56a of the switch 56 to the television receiver 70. During other modes other than the reproduction mode, the moveable contact 56c of the switch 56 is connected to the fixed terminal 56b so as to supply the signal which is applied to the input terminal 51 to the television receiver 70. Thus, the signal reproduced from the VTR can be received and reproduced by the television receiver 70 and also the standard broadcast signals can be received by the television receiver under this condition.
In the circuit arrangement of the prior art, however, when the VTR is placed into the reproduction mode and the television receiver 70 is tuned to the vacant channel to allow watching of the reproduced signal on the television receiver, in the event the user forgets to move the moveable contact 56c to the fixed contact 56a at the output of the RF converter 55, a reproduced signal from the converter 55 will not be supplied to the television receiver 70 and thus a picture and sound will not be reproduced on the television receiver and only noise signals will occur which is undesirable.
Thus, in the prior art circuit arrangement, a switching control circuit 57 is usually provided to automatically control the switch 56. In such system, during reproduction mode, a signal is generated when the VTR is in a reproduction mode and such reproduction mode signal is applied to an input terminal 58 of a control circuit 57 so as to automatically cause the moveable contact 56c of the switch 56 to be moved to the fixed contact 56a to connect the output of the RF converter 55 to the television receiver during the reproduction mode of the VTR. If the switch 56 is controlled by the control circuit 57 so as to automatically switch the moveable contact 56c to the fixed the contact 56b which is connected to the input terminal 51 at the instant when the reproduction mode ends, when the television receiver 70 is tuned to the signal of the vacant channel, the television receiver will be supplied with the signal from the antenna which results in a signal having a high noise level being reproduced by the receiver 70. So as to prevent this mode of operation, the switch 56 is usually controlled by the control circuit 57 so as to connect its moveable contact 56c with the fixed terminal 56a at the output of the RF converter 55 only when the reproduction mode is again detected and the switch 56 is controlled by the control circuit 57 so that the moveable contact 56c is connected to the fixed terminal 56b which is connected to the input terminal 51 by supplying a manual operating signal to an input terminal 59 of the control circuit 57. The signal to the input terminal 59 may be supplied by a television/video switching control button or by a switch, not shown.
Recently, television receiver 70 have been designed to have line input terminals in addition to an antenna input terminal for the RF signals wherein composite video baseband video and baseband audio signals can be directly applied to the receiver so as to directly supply the video and audio signals in a baseband level. In such receivers since the video signal and the audio signal at the input of the RF converter 55 are respectively supplied to line output terminals 61 and 62 and such signals are supplied to the input terminals of the television receiver 70 and, thus, there is a less risk that such signals will be deteriorated by conversion and such signals can be accurately reproduced and received at the television receiver. During such operation, the antenna terminal of the television receiver 70 should also be connected to the RF output terminal 60 of the VTR so as to receive the RF signal from the input terminal 51.
In other words, the optimum RF signal should be supplied to the VTR when it is intended to record a signal. For this purpose, it is conventional that the television receiver 70 is connected to the RF output terminal 60 of the VTR and a distributor is provided at the stage before the tuner 52 of the VTR.
However, according to this described connection when the VTR is once placed in the reproduction mode, although the television receiver 70 is not conditioned to receive the signal of the vacant channel, the moveable contact 56c of the switch 56 is automatically connected to the fixed contact 56a at the output of the RF converter 55. Thus, the user must operate the television/video switching control button again so as to receive any selected broadcast channel with the television receiver after the reproduction mode has ended. Thus, the operating characteristic of the apparatus is not satisfactory.
According to the prior art described above, when the base band video and audio line output terminals of the VTR are connected to the line input terminals of the television receiver and the RF output terminal of the VTR is connected to the antenna terminal of the television receiver, if the VTR is set to the reproduction mode, the RF output terminal will unnecessarily be switched to the RF converter output. As a result, when the reproduction mode of the VTR ends the user has to manually perform an extra operation so as to obtain the original state of the switch which considerably deteriorates operation of the system.